a) Field of the Invention
The present invention relates to a non-flexible endoscope to be used widely in the medical field, and mainly a non-flexible endoscope which can be manufactured at a cost low enough to be disposable.
b) Description of the Prior Art
In the recent trend of surgical operations in the medical field, medical techniques are exercised increasingly in conditions of minimum contacts with higher parasites by using endoscopes and treating tools developed exclusively for operations in such conditions. Since affected parts which conventionally required laparotomy for medical treatments can now be treated in the conditions of minimum contacts with the higher parasites under observation through endoscopes for lessening burdens of patients by reducing days of hospitalization, etc., further development is expected for the surgical operations under observation through endoscopes.
Dependently on structures of insert sections of endoscopes which are to be inserted into body cavities, the endoscopes are classified into two types: flexible endoscopes and non-flexible endoscopes. Out of these two types, the non-flexible endoscopes which provide images of higher qualities are used for surgical operations under observation. The non-flexible endoscopes has another merit that they are bearable of autoclaving.
In the recent days where a serious problem is posed by hospital infections, it is remarkably important to sterilize medical tools and instruments, and autoclaving apparatuses are more widespread than the other types of sterilizers. It is therefore necessary to configure the endoscopes so as to have structures bearable of autoclaving.
For the non-flexible endoscopes which have no flexible section, it is rather easy to select materials and structures which are bearable of autoclaving. It is therefore general in practice to repeatedly use non-flexible endoscopes bearable of autoclaving while sterilizing these instruments after individual uses.
On the other hand, attempts are made to configure the non-flexible endoscopes themselves so as to be disposable for preventing hospital infections from being caused through repeated use of the non-flexible endoscopes. In order to configure the non-flexible endoscopes so as to be disposable, it is necessary to configure them so that they can be manufactured as low costs while maintaining practical utilities thereof.
FIG. 1 shows a conventional non-flexible endoscope and an observation optical system used therein. The conventional optical system of this conventional non-flexible endoscope consists of a short objective lens system O disposed in a leading end of an insert section 1 to be inserted into body cavities and a relay lens system R disposed in the insert section 1 almost over the entire length thereof, and an eyepiece lens system E disposed in a grip section 2: these lens systems being integrated with one another in a main body of the non-flexible endoscope.
This conventional non-flexible endoscope is configured so as to permit observing, through the eyepiece lens system E, an image which is formed by the objective lens system O and relayed ordinarily in three cycles by the relay lens system R. This relay lens system consists of fundamental lens units each being symmetrical with regard to a vertical axis perpendicular to the right-to-left direction and is configured so as to relay an image in a plurality of cycles.
It is for the purpose of obtaining required brightness in an optical system that an image is relayed in a plurality of cycles in the optical system for the non-flexible endoscopes such as the conventional example described above.
Since insert sections of non-flexible endoscopes have small outside diameters and large effective lengths, it is necessary for maintaining brightness of images transmitted through the insert sections to enlarge numerical apertures of relay lens systems by increasing numbers of relay cycles. In case of an optical system which uses an insert section having a given effective length in combination with a relay lens system having a given fundamental composition and a given outside diameter, a numerical aperture of the relay lens system is determined dependently on a length required for a single relay cycle and therefore proportional to a number of relay cycles to be performed by the relay lens systems.
The conventional non-flexible endoscope shown in FIG. 1 hardly allows the main body thereof to be disposable due to a fact that the relay lens system R used for composing the optical system thereof comprises a large number of lens elements and the optical system requires too high a manufacturing cost. When the manufacturing cost of the optical system is reduced simply by reducing the number of relay cycles or the number of the lens elements disposed in the relay lens system as a whole, the length required for a single relay cycle is shortened, thereby reducing the numerical aperture of the relay lens system.
For the reason described above, the optical system for the conventional non-flexible endoscope does not allow to lower the manufacturing cost thereof while reserving the brightness required therein.